climb and dive valve

"Temperature/Altitude/Humidity Test Chambers
Temperature/Altitude/Humidity chambers are typically used to simulate test conditions for components and subassemblies designed to meet military specifications and/or for use in aeronautical, space engineering, automotive, computer, electronics, packaging, and meteorological fields.
...
Envirotronics EA (temperature and altitude) and EAH (temperature, altitude,
and humidity) chambers are designed to allow the user to perform temperature,
humidity and altitude condition testing in one combined test chamber. More
than one condition can be created simultaneously to satisfy many types
of test requirements. Our EA and EAH Series chambers are designed to
simulate altitude conditions up to 100,000 feet. They are also designed to
offer simultaneous temperature/altitude testing from site altitude to 35,000
feet. Humidity tests can be conducted at site altitude only.
...
Vacuum System
• The internal altitude is controlled using pneumatically controlled climb and dive valve"
http://www.envirotronics.com/pdf/eah.pdf